FOOD REQUIREMENTS 477 



I. Phototrophic nutrition is characteristic of chlorophyll-bearing 

 species, which utilize the energy of light in photosynthesis. Some appear 

 to be obligate phototrophs, while others may be grown in darkness under 

 suitable conditions. On the basis of nitrogen requirements, several va- 

 rieties of phototrophic nutrition may be recognized: 



( 1 ) Photoautotrophic nutrition is characteristic of species which can 

 grow in inorganic media; Chlorogoyiium euchlorum (Loefer, 1934; Hall 

 and Schoenborn, 1938a) is typical. No obligate photoautotroph is known. 



(2) Photomesotrophic nutrition is that in which one or more amino 

 acids serve as nitrogen sources. In Euglena deses (Dusi, 1933b) this 

 seems to be the simplest possible method of nutrition. Photomesotrophic 

 nutrition may also be carried on by facultative photoautotrophs. 



( 3 ) Photometatrophic nutrition is characteristic of species which grow 

 in peptone solutions or comparable protein media. Euglena pisciformis 

 (Dusi, 1933b) has been described as an obligate photometatroph. This 

 type of nutrition may also be carried on by facultative photoautotrophs 

 and photomesotrophs. 



II. Heterotrophic nutrition is characteristic of species which have no 

 chlorophyll and hence require an organic carbon source. Some chloro- 

 phyll-bearing species have been grown in darkness and may, in this sense, 

 be considered facultative heterotrophs. On the basis of nitrogen require- 

 ments, three varieties of heterotrophic nutrition may be distinguished. 



(1) Heteroautotrophic nutrition involves utilization of inorganic 

 nitrogen compounds in the presence of an organic carbon source. Poly- 

 toma uvella (Pringsheim, 1921; Lwoff and Dusi, 1938a) and Astasia sp. 

 (Schoenborn, 1938) are examples. 



( 2 ) Heteromesotrophic nutrition: growth requirements may be satis- 

 fied by one or more amino acids as sources of nitrogen and carbon. 

 Growth is usually much more vigorous with an additional carbon source, 

 such as acetate. Polytomella caeca (Pringsheim, 1937a, 1937c) is repre- 

 sentative. 



(3) Heterovietatrophic nutrition is characteristic of organisms which 

 grow in peptone solutions or similar media. Obligate heterometatrophs, 

 such as Hyalogonium klebsii (Pringsheim, 1937b) and Glaucoma piri- 

 formis (A. Lwoff, 1932), cannot be grown in amino-acid solutions or 

 simpler media. This type of nutrition is exhibited by various holozoic 

 Protozoa (ciliates, amoebae) which have been grown in pure culture. 

 Among the parasitic flagellates, certain Trypanosomidae (M. Lwoff, 



